Astrodemia — Learn the Night Sky
Astrodemia is a free, Duolingo-style web app that teaches you to recognize the constellations and the brightest stars through a few minutes of practice a day. Its Bortle-adaptive curriculum starts with what you can see from a light-polluted city and builds toward what you will see under a truly dark sky.
What you learn
All 88 IAU constellations; 28 bright named stars, from Sirius, Canopus and Arcturus to Vega, Betelgeuse, Antares and Polaris; and 11 asterisms and sky skills: Orion's Belt, the Big Dipper, the Pleiades, the Great Square, the Summer Triangle, the Spring Triangle, the Winter Hexagon, star-hopping, reading magnitudes, telling planets from stars, and how the sky turns with the seasons.
How it works
A session goes straight to questions — there is no tutorial — and takes a few minutes. Fifteen quiz types unlock as you master each item, from multiple choice with the figure drawn in to finding a constellation unaided: Name This (with the lines, then without), Spot the Star, Is This?, Spot the Constellation, Star's Home, Circle It, Type It, Connect the Stars, Naked Eye, Star Hop, Rotated Sky, Near or Far, What's Missing and Speed Round. FSRS, the open-source spaced-repetition scheduler that Anki also offers, decides when each item comes back.
A constellation your sky can show only counts as mastered once you have found it in Naked Eye — no lines drawn, sixty seconds on the clock — twice in a row.
Made for city skies
Pick your city and Astrodemia reads its light pollution from the World Atlas of Artificial Night Sky Brightness, or set your Bortle class by hand. The practice sky is dimmed to match, the constellations bright enough to survive the skyglow come first, and the ones that need a darker site are marked rather than hidden.
Free, private and offline
Astrodemia is free, with no ads and no sign-up. Your progress is stored on your device; an optional Google account backs it up and syncs it between devices, and you can export everything as a JSON file at any time. After the first visit it works offline, and on a phone it can be added to the home screen like an app. It speaks English, Español, 中文, 日本語, 한국어, Français, Deutsch and Português.
Common questions
How do I learn the constellations from a light-polluted city?
Start with the constellations your own sky can actually show. Tell Astrodemia which city you observe from and it reads that city's light pollution off the World Atlas of Artificial Night Sky Brightness, then moves the patterns bright enough to survive the skyglow — Orion, the Big Dipper, Cassiopeia — to the front of the queue. The practice sky is dimmed to match, so what you drill is what you will find when you look up. Constellations that genuinely need a darker site are marked rather than hidden, so you know what is waiting on your next trip out of town.
What is the Bortle scale?
A nine-step scale for how dark a night sky is. Class 1 is a pristine site where the Milky Way casts shadows; class 9 is an inner-city sky with a few dozen stars in it. Each step up costs you roughly half a magnitude of faint stars, which is why the same constellation can be obvious from a village and invisible from a suburb. Astrodemia uses your class to decide which stars are drawn in the practice sky and which lessons come first. Set it by hand, or pick your city and let the light-pollution atlas set it for you.
How long does it take to learn the night sky?
One session is enough for your first constellation — that is why Astrodemia opens with questions instead of a tutorial. The full catalogue is 88 constellations, 28 named stars and 11 asterisms and sky skills, and that is a project of months, partly because the sky sets the pace: a winter constellation can only be confirmed in winter. A session is twenty questions and takes a few minutes, and the spaced-repetition schedule decides when each thing comes back, so the number that matters is days practised, not hours spent.
Do I need a telescope?
No. Everything Astrodemia teaches is naked-eye: the star catalogue stops at magnitude 6.5, roughly the limit of a dark-adapted eye, and the questions ask you to recognise patterns rather than to hunt faint objects. Binoculars are a pleasure on the Pleiades or the Beehive but are never required, and practising needs no equipment at all — the app runs in a browser, indoors, at any hour of the day.
How is Astrodemia different from a star-map app?
A star-map app tells you what your phone is pointing at; Astrodemia teaches you to know it without the phone. Star maps are excellent references, but looking something up does not make it stick. Astrodemia quizzes you on the patterns themselves — naming them, tapping them, drawing them — and uses spaced repetition so each one comes back just before you would forget it. The aim is the moment you step outside, look up and recognise Orion without reaching for anything.
Is Astrodemia free, and do I need an account?
It is free, has no ads, and never asks you to sign up: the whole app works without an account, keeping your streak, your XP and every spaced-repetition card in your own browser's storage. If you want a backup, you can sign in with Google from Profile, and your practice records are then kept on Astrodemia's server and synced to your other devices. Without an account, nothing about your progress leaves your device unless you export it yourself — as a JSON file you can keep or import on another device.
Does Astrodemia work offline, and on a phone?
Yes to both. It is a website, so there is nothing to install, though you can add it to a phone's home screen and it will open like an app. After the first visit a service worker keeps the app, the star catalogue and every language on the device, so a session runs with the network switched off. That is deliberate: the darkest skies are usually the places with the worst signal.
Questions or feedback: [email protected]